Temperature responsive devices, bimetallic coils for use therein, and blanks for making such coils



Oct. 23, 1951 H sc 2,572,059

TEMPERATURE RESPONSIVE DEVICES, BIMETALLIC COILS FOR USE THEREIN AND BLANK-S FOR MAKING SUCH COILS Filed March 11, 1947 3 Sheets-Sheet l attorneg s Oct. 23, 1951 H. SCHLAICH 2,572,059

. TEMPERATURE RESPONSIVE DEVICES, BIMETALLIC COILS FOR USE THEREIN AND BLANKS FOR MAKING SUCH COILS Filed March 11, 1947 3 Sheets-Sheet 2 \IIII/I/ HER/VAN jam A/(H I Zinnentor l a attomegs H. SCHLAICH TEMPERATURE RESPONSIVE DEVICES, BIMETALLIC COILS FOR USE THEREIN AND BLANKS FOR MAKING SUCH COILS 3 Sheets-Sheet 3 Filed March 11, 1947 (Ittornegs Patented Get. 23, 195% UNITED STATES PATENT 'OF'FIC'E I 2,572,059 I TEMPERATURE RESPONSIVE DEVICES, nr-

,METALLIC COILS ron use 'rnmmm, AND numxs ron MAKING soon cons Herman Schlaich, Elmhurst, N. Y.

Application March 11. 1947, Serial No. 733,944 p In Switzerland October 1, 1946 In the making of temperature-responsive instruments and devices, it is important to utilize a temperature-responsive element which is compact so that it takes up little room and can be located as near as possible to the optimum position for responding to the temperature conditions by which it is intended to be influenced. It ls also important to utilize a temperature-responsive element of such nature that it will respond quickly to temperature changes. For this reason it is important that the element be in close thermo-conductive relationship with the surrounding medium, the temperature of which is to be indicated or which is to influence the operation of the device. This result will not be secured, for example, if the temperature-responsive element is of such nature that the thermo-responsive member such as the bimetallic coil is so wound that it must be enclosed in a loose fitting shell or casing which will space the coil a substantial distance from actual contact with the medium to the temperature of which the coil is intended to respond. It is also important, if the instrument or device is of such nature that any substantial force is required to operate it, that the temperature-responsive element shall have sufiicient power to cause a firm and positive operation of the device. For example, in case the thermometer which is used under severe operating conditions, the thermometer pointer may be subject to vibration due to shock. This is particularly noticeable in the case of thermometers or thermostatic devices used to close electric contacts. In such devices if the contact is not firmly closed and held closed, vibration will cause separation of the contacts and consequent arcing and false reading or improper operation of the control devices. With the foregoing considerations in view, it is an object of the present invention to provide a temperature-responsive element including a. bimetallic coil, the construction of which is such that great rapidity of action is assured. The coil is of compact form so that it may be located at theexac't location where best operation will be secured. The form of the coil also permits it to be madeof such dimensions as to secure ample power for operation of mechanical devices for closing or opening of electricalcontacts, 'etc.

Another object of the invention is to provide a coil construction and blank'for making the same by which coils of the desired form may be quickly and easily made out of bimetallic material having the characteristics necessary for securing, rapid and eflective operation. In order to secure rapidity and sensitiveness in operation in a bimetallic temperature-responsive device, it is important that as thin a bimetallic strip as possible be utilized and that the strip be coiled in as compact form as is practicable. If the bimetallic material is thick, it takes longer for temperature changes to affect it and, therefore, it is sluggish in operation. Furthermore, it cannot be coiled into as compact form as a coil of very thin material. Therefore, when embodied in a temperature-responsive element, it is necessarily enclosed in a casing of relatively large volume and cannot be so responsive to changes in temperature in the ambient fluid. Another characteristic of bimetallic coils is that their power depends upon the width of the strip of which the coil is made rather than upon the thickness. In order to secure substantial power, therefore, a wide strip must be used.

In accordance with the present invention, a bimetallic coil is provided which is closely wound of very thin bimetallic material, the coil being of such form that it may be formed ofmaterial of very much greater width and thickness without departing from a coil form of minimum overall dimensions. The form of coil best suited to accomplish the objects above set forth is made of a bimetallic metal of Very thin gauge, which is formed into blanks of such shape that it is possible to coil the blank into a double coil starting from the inside at one end andcoiled for a number of turns in a spiral around a central axis to a bridge section at the middle of the blank, the end of the blank beyond the bridge section being coiled progressively inward in a spiral,the two coil portions being in axial alignment. By forming the coil out of very thin bimetal of substantial width, the coil is given ample power to properly operate the instrument or device, and at the same time the total dimensions of the coil are kept at a minimum. The center convolution of each coil portion is wound closely about a driving or driven shaft as the case may be, the end of such convolution preferably being fitted in a shallow recess at one side of the shaft in which it may be firmly secured by welding. With such a construction, shafts of minimum diameter may be utilized and there is no waste space in the center of the coil. {The double coil constru'ction is, also char acterized by a very slight change in outer diam-j eter as the coil expands or contracts because the expansion or contraction of the two coil parts to a certain extent offset each other in so far as expansion or contraction in diameter are concerned, although the effect of the two coil portions is cumulative in producing rotative movement of the driven shaft. A suflicient number of convolutions may be embodied in a very compact form to secure rotation of the pointer or movable element of the device through as much as 360 degrees.

Owing to the fact that the coil has comparatively little expansion in cimcumference it may be enclosed in a shell fitting the coil with but slight clearance. Thus, the enclosing shell constituting the exposed surface of the thermo-responsive element is of minimum dimensions and is close to the bimetallic coil and the latter is, therefore, quickly influenced by the temperature of the liquid or fluid medium in which the temperatureresponsive element is located. Preferably, the casing is filled with a liquid of good heat transmitting properties, such as oil or glycerin so as to transfer the heat as quickly as possible from the enclosing shell to the coil itself.

An important feature of the invention comprises the blank of thin bimetallic material of such shape that it may readily be coiled into the double coil form desired.

Other objects and advantages of the invention will appear in the course of the following description of certain preferred embodiments chosen to illustrate the principles thereof.

In the accompanying drawings,

Fig. 1 is a side elevation of an indicating thermometer embodying one form of temperature-responsive element;

Fig. 2 is a view of the face of the thermometer shown in Fig. 1;

Fig. 3 is a central longitudinal section of the thermometer head on an enlarged scale;

Fig. 4 is a central longitudinal section of the temperature-responsive end of the thermometer on a still further enlarged scale;

Fig. 5 is a transverse section taken on the line 5-5 of Fig. 4 on a further enlarged scale;

Fig. 6 is a plan view of a blank utilized for making the bimetallic coil of the form shown in Figs. 1, 4 and 5, the scale being the same as that shown in Fig. 1, which is approximately full size;

Fig. 7 is a plan view of a strip of bimetallic material showing how the blanks of the form shown in Fig. 6 may be cut therefrom;

Fig. 3 is a plan view of a modified form of blank;

Fig. 9 is a view partly in horizontal section of the head of a contact closing thermometer;

Fig. 10 is a longitudinal section of the thermometer shown in Fig. 9, the section being taken on line Ill-l0 of Fig. 9;

Figs. 11 and 12 are plan views showing how blanks for forming double coil bimetallic elements may be formed from a straight strip of bimetallic material;

Figs. 13 and 14 are plan views showing another 65 way of forming the blanks out of a straight strip of bimetallic material;

Fig. 15 is a plan view of a blank for forming another form of duplex coil;

Fig. 16 is a horizontal section of a coil made 70 4 Fig. 18 is a perspective view of the coil shown in Fig. 18.

In illustrating the-bimetallic metal in the drawings. no attempt has been made to show the two layers of metal separately, because of the smallness of the scale, except in Fig. 5 which has been enlarged sufficiently to permit illustration of the two layers of 'metal. Itis to be understood, that in all cases the coils and the blanks for making the same are, to be made of two permanently united layers of metals having different coefflcients of expansion whereby the metal will be caused to warp or change its shape when subjected to changes in temperature.

Referring to the form of instrument shown in Figs. 1 to 5, these figures illustrate a simple form of thermometer having a head 20, a stem 22 and a "bulb" or thermo-responsive end 2!. Inside of the casing 26 of the thermo-responsive end of the thermometer is a double coiled bimetallic element 23. This element comprises two axially aligned coiled portions 30 and 32 which are connected by a bridge convolution 3|. The inner convolution of the coil portion '33 is secured to a fixed shaft 35 which may be supported in any suitable manner as by being tightly fixed in a cap or plug 38 which is sealed in the lower end of the shell or casing 26. The end of the inner convolution is preferably secured to the shaft by providing in the latter a longitudinal groove or depression having a helicallv curved wall portion 40 and an end wall portion or shoulder 42, the wall portion 40 curving inwardly from the cylindrical surface of the shaft with which it mer es towards the bottom of the shoulder 42 so that the groove increases in depth towards the shoulder. The shoulder 42 is preferably the same height as the thickness of the bimetallic material, the end of which is secured in the groove preferably by welding. with this construction, the bimetallic coil springs from the shaft, so to speak, in a smooth curve and it may be coiled around the shaft with only the minimum clearance necessary to enable one convolu- 45 tion to escape actual contact with the next.

The dimensions of the coil may thus be kept to an absolute minimum. Furthermore, as the groove in the shaft does not weaken it substantially as would be the case if the shaft were transversely slotted, the diameter of the shaft itself may be kept to a minimum which assists in reducing the maximum diameter of the coil. The center convolution of the coil portion 32 is secured to the end of a rotatable arbor H in the same manner as the end of the coil portion 3|! is 6 dicating hand It. which is mounted to move over the graduated dial 43 in the instrument head. In the construction shown. the instrument head is covered by a crystal 50 which is secured in place by a bezel ring 52, a'packing ring 54 being preferably provided so as to hermetically seal the chamber in which the indicating hand moves.

It is to be noted that with the double coil construction, both ends of the double coil are located near the axis of the coil. This permits the free end of one coil portion to be anchored to a central fixed shaft 36, while the inner end of the other coil portion is anchored to the end of the movable arbor II. The shaft 36 and arbor H are mounted in axial alignment. There is no 7 outer free end. of the coil which has to be anchored to a support outside of the cell. This gives a very simple structure and also permits the coil to be enclosed in a shell closely surrounding the coil with a minimum of clearance. If it were necessary to provide an anchor for the outer free end of the coil between the outer convolution of the coil, and the shell, the shell would have to be spaced much further away from the coil than in the construction of the invention.

The bimetallic temperature-responsive element 28 is preferably formed of very thin bimetallic material. A bimetallic metal of a thickness in the neighborhood of five one thousandths of an inch (0.005") is satisfactory for most instruments embodying the present invention. By using a bimetallic material of this order of thickness in the form of a relatively wide strip, very substantial power is developed when the coil is subjected to changes in temperature so that a firm and positive action is secured and the instrument will not be objectionably influenced if subjected to vibrations. For example, in the instrument shown in Fig. 1, the bimetallic strip 7 may be approximately A" in width. This gives a ratio of strip width to thickness of approximately 50 to 1. In instruments where still greater power is required, a much wider strip may be used. It is perfectly practicable to use a strip an inch in width, or two hundred times the thickness of the strip. With such a construction, greater power is developed and the bimetallic element may be used to close contacts or move relatively resistant instrumentalities. A bimetallic coil of the character described can in many instances be substituted to do the work of a liquid filled thermostatic element having a large bulb and expansible bellows, such as would occupy many times the space and involve many times the cost of the bimetallic coil.

Owing to the nature of the bimetallic metal, and the relatively greater width of the metal with relation'to its thickness of the metal, it is not possible to wind a coil of the formdescribed from a simple straight strip of material as has been customary in the making of bimetallic coils. Anyattempt to wind a double coil of the character shown out of bimetallic material having the characteristic dimensions described would result in tearing or completely deforming the strip and would also result in setting up such internal stresses therein as would prevent its proper functioning.

In accordance with the present invention, therefore, an offset blank is first formed of the bimetallic material, the shape of the blank being such that it may be wound into the double coil portions 30 and 32 connected by the bridge convolution 34. One preferred form of blank is il-' lustrated in Figs. 6 and 7. As shown in Fig. 6, the blank comprises two longitudinally-extending ends which are coiled to form the coil portions 30 and 32 and are, therefore, designated by numerals 30 and 32, respectively, these two portions being ofiset slightly more than the width of the strip so that when they are wound into coil form there is a slight clearance between the two coils and which is indicated at 56 in Fig. 4. The end portions 30 and 32 are connected by the bridge convolution portion 34, which .may be diagonal, curved or av straight transverse portion (Fig. 8). The blanks are preferably so formed as to have the grain of the metal resulting from =;the direction in which it is rolled extend longitudinally of the blank. To accomplish this'resalt, blanks may be cut from a rolled strip of the material in accordance with thelayout shown in Fig. 7. This will result inthe blanks havingthe grain extending longitudinally. and will "leave claimed in this case.

little waste. The particular forms of blank illustrated in Figures 6, '7 and 8 and of the coils formed therefrom form the subject matter of a divisional application, Serial No. 207,890, filed by me January 11, 1951, and are therefore not In some instances it may be more economical to form the blanks from a straight strip of material. One method oi accomplishing this is shown in Figs. 11 and 12. Fig. 11 shows the straight strip of material provided with a series of V-shaped notches 60 in one side thereof and a similar series of notches 62 in the other side. These two series are offset longitudinally to permit the strip to bebent in one direction opposite one series ofnotches and in the opposite direction opposite the other series of notches as shown in Fig. 12 so that an offset blank isformed similar in shape to that illustrated in Fig. 6. This blank may then be coiled into the form of coil shown in Figs. 1, 4 and 5.

Figs 13 and 14 show another way of forming an oflset blank out of a straight strip of material. As here illustrated each end of the strip is bent aboout a 45-degree line (Stand 68) so as to provide two offset strips extending from a central bridge portion 10. One part of the strip is bent over in one direction and the other .in the opposite direction. Thus the bimetallic elements of the two strip portions retain their original relationship so that the effect of the two coils is cumulative as in the constructions already described. a I I By using the blanks comprising the parallel oilset end portions, as shown in Figs. 6, 8, 12

and 14, it will be seen that the end portions may' be coiled by a straight winding operation into a the double coil formation shown in Figs. 1, 4 and 5. Such coiling involves no lateral deformation of the strip and, therefore, does not tear or tend to distort the same in an objectionable manner.

Furthermore, it permits the use of strips of any desired width so that a bimetallic coil may be produced capable of exerting great force when subjected to temperature change.

The double coil with the two parts connected by the bridge convolution has the characteristic that it isconstrained by the bridge convolution against expansionin diameter to any great ex- I tent, almost the total force of the expansion being translated into rotary movement tending to rotate therotatable arbor of the instrument. This produces the maximum turning movement of the pointer and also results in the coil havin very small expansion in diameter. The latter characteristic is very important as it permits extreme rapidityto temperaturejchanges. I In the construction'shown in Figs. l to 5, the

temperature-responsive"end of the instrument 24 *comprises ajthinfmeial [casing 26, one end of which is "closed, by the cap or plug" 38- andfthe other'end of which'is 'for'med'intofa neck-80,10! reduced diameter which is welded orotherwise secured to the tubular stem 22. order to keep as much of the liquid as possible from leaking into the stem, the end of the stem is provided with a valve seat 62 against which rests a valve washer 04 having a flat face fitting against the valve seat. The washer 64 may be yieldingly pressed against the valve seat by a, light coiled spring 00. the other end of which bears against a washer l surrounding the arbor and resting against the end of the bimetallic coil. As the washer 84 has a flat face, it may slide laterally over the valve seat in case the arbor is moved out of exact axial alignment with the axis of the tubular stem 22.

Thus the arbor will rotate freely without binding at all times. The valve washer 64 need not be absolutely tight because the liquid in the easing cannot pass all the way up the tubular stem if the head of the instrument is tightly sealed. In such case, the air is trapped in the head of the instrument inside of the siem and, therefore, prevents the liquid from passing freely into the instrument head irrespective of the position of the thermometer. However, the use of the valve washer is desirable to help in keeping the liquid out of the stem and confining it in the easing surrounding the bimetallic coil.

The bimetallic coil of the present invention finds particular utility in an instrument or apparatus in which more force is required to be exerted than in the case of an ordinary indicating thermometer. For example, it is parlicularly useful in connection with contact thermometers which are arranged to close or open a contact upon reaching a particular point. Figs. 9 and show a maximum and minimum contact thermometer embodying the invention. In Fig. 10, 24 is the thermo-responsive element or bulb of the thermometer which contains a bimetallic coil of the form shown in Figs. 1, 4 and 5. The bimetallic strip may, however, be wider so as to have more power. This coil turns the arbor 44 inside of the stem 22. In the construction shown, the pointer of the thermomeier which is turned by the arbor forms one of the electric contact elements and is, therefore, insulated from the arbor. As shown, the arbor carries a flange I00 at its upper end on which is fixed an insulating flange I02 carrying an insulating bushing I04 surrounding the projecting end of the arbor. A sleeve I06 surrounds the bushing and is provided with a flange I08 which is fastened to the insulating flange I02 by a screw IIO. Another screw II2 secures the insulating flange to the arbor flange I00. The sleeve I06 and flange I08 are thus rotated by the arbor. The instrument pointer H4 is carried by the flange I00. Attached to the sleeve I06 is a hair spring II6, the outer end of which is fixed to an-arm I I0, mounted in the easing I20 of the instrument but insulated therefrom. The end of a wire I 22 is electrically connected to the arm I I0 so that the pointer I I 4 is in electrical connection with the wire through the sleeve I06, hair spring H6 and arm H6. The pointer II4 carries a contact pin I24. Maximum and minimum contact hands are adjustably mounted in the casing. A maximum contact hand I30 is mounted on a pivot screw I02 which is carried by a bar I34 carried by the instrument casing but insulated therefrom. A wire I36 carries current to the arm I34. A hair spring I" is connected to the hub of the hand I30, the outer end of the hair spring being connected to the arm I34 so that the hair spring conducts current from the arm to the hand. For adjusting the hand, the latter is provided with an extension I40 which rests against a pin I42 carried by an adjusting crank I44 mounted on a rotatable stud I46 carried in the casing. The stud has a slotted head I by which it may be set so as to cause the crank pin I42 to push the extension I 40 of the hand I00 against the tension of the hair spring I00 to its desired position of adjustment. The hand I30 is capable of limited movement on the stud I40 to which it is yieldably attached by a relatively stiil' spring I50. The spring I50 holds the hand in the position of adjustment determined by the rotation of the stud I46 but will permit limited movement of the hand when engaged by the contact pin on the pointer I I4 so as to prevent bending or breakage of the parts. The hand I00 is provided with a knife edge I52 forming a contact edge for engagement with the pin on the pointer. The minimum hand I54'having a contact edge I56 is mounted on the pivot screw I50 carried by the arm I60 which is connected to the lead wire I02. A rotatable stud I64 mounted in the casing is connected to a crank arm I66 which carries a crank pin I68 engaging in extension I10 on the arm I54. The hand I54 is connected to the arm I60 through hair spring I12. By using a double bimetallic coil of sumcient width of material as the thermo-responsive element of the thermometer, the pointer II4 will be moved with suillcient firmness to cause the pin I24 to bear against one or the other of the knife edges I52 or I56 with enough pressure to make a good contact and such contact will be steadily maintained and the pin will not be moved out of contact due to vibration. With a weak bimetallic spring of narrow width, such as has heretofore been usually employed in bimetallic thermometers, satisfactory contact cannot be maintained in this manner.

Figs. 15 to 19 show another form of bimetallic coil and the blank for making the same possessing some of the characteristics of the bimetallic coll already described. In accordance with this construction a duplicate bimetallic coil is provided which, however, is not formed of a single oil'set blank, but is formed of two parallel strips of bimetallic metal, one of which is reversed with respect to the other strip. That is to say, one strip has the metal of greater coefilcient of expansion on the outside and the other strip has the metal of greater coefficient of expansion on the inside.

Fig. 15 shows the two strips 200 and 202 with one reversed with respect to the other, as described, the two strips being spaced slightly apart and firmly united at their outer ends. In the construction shown, the strip 200 has an car 204 at the one side of its outer end which is welded at 206 to the corner of the other strip 202. The inner end 208 of one of the strips, for example, strip 200, is welded to the arbor 44 of the thermometer, as shown in Fig. 16, while the inner end of the strip 202 is welded to a fixed shaft (not shown). The two strips are coiled in the same direction from inside to outside, so that a double coil is provided, the united ends of the two coils forming a free or unanchored end 2I0. Owing to the fact that the two coils are reversed with respect to the coeflicients of expansion of the metal layers, the effect of the two coils is cumulative, thereby producing double the rotation of the arbor from that which would be obtained if a single coil were used.

In a coil of the kind shown in Figs. 15 to 18, the outer convolutions tend to expand outwardly to a certain extent so that the total diameter of the coil enlarges somewhat. This movement is ammo ward movement of the outer turns and particularly of the'free end Ill and adjacent parts of the coils. it is desirable to stiiien the on r parts oi the strips so as to reduce such outwar \movementand cause the expansive effect of thev blmetallic metal to exert itself'as far as possible in rotating the arbor. This stiffening of the outer convolutions is preferably progressive, being at maximum near the free end of the coil and decreasing inwardly. In the construction shown,

this progressively stiiiening effect is accomplished by pressing a tapered rib from the metal of each strip, such ribs being indicated at 2|! and Ill. These ribs are larger and, therefore, stiller nearthe outer ends of the coil. In this construction, as well as that previouslydes'cribed, a very compact bimetallic element is produced and one in which the bimetallic material may be of any desired width, thereby making available any operating force necessary. Both parts ofjthe coil are, furthermore, mounted onjshafts attached to their inner ends, resultingin' ve'ryfe'asy and efllcient mounting of the coil. It is unnecessary to connect the free outer end of the coil to the shell of the instrument or any other support in the outside of the coil. I 1

While I have illustrated and described in detail certain preferred forms of my invention, it is to be understood that changes may be made therein and the invention embodied in other structures. I do not, therefore, desire to limit myself to the specific construction illustrated, but intend to cover my invention broadly in whatever form its principles may be utilized.

. What is claimed is:

l. A blank of bimetallic metal for forming into a double coil composed of two parallelspirally wound portions connected by a bridge portion, said blank being much wider than its thickness and comprising two straight parallel coil-forming portions offset laterally by an amount slightly wider than the width of said portion, said parallel portions being connected by a bridge-forming portion, said blank being formed from a straight strip of metal having a series of notches cut in each edge thereof, said two series of notches end of one coil portion being wrapped around the outside of a fixed shaft and fixed thereto and an inner end of the other coil portion being wrapped around the outside of an arbor and fixed thereto,

v said shaft and arbor having grooves therein bounded at one sideby shoulders of a height approximately equal to the thickness of the bimetal, the bottom walls of the grooves curving 10 metallic material of much greater width than thickness, said coil comprisingtwo coaxial coil portions having their outer convolutions connected by a bridge member, the inner convolution of. one coil portion surrounding and being attachedto said shaft and the inner convolution on the other coil portion surrounding and being attached to said arbor, and liquid sealing means around the .arbor at a point where the arbor en ters the casing, said casing being filled with a heat conducting liquid.

4. A temperature responsive device comprising a stem, a casing of heat conducting material mountedon said stem, a closure for the outer end of said casing. an arbor rotatably mounted in the stem and having its end projecting into the casing, a shaft carried by the closure at the end of the casing, said shaft projecting into the casing towards the end of said arbor and in axial alignment therewith, a duplex bimetallic coil wound from a strip or bimetallic material of much greater width than thickness, said coil comprising two concentric coil'portions having their outer convolutions connected by a bridge memsurrounding and being attached to said arbor,

out in a spiral, said grooves receiving the inner ends of said coil portions.

3. A temperature responsive device comprising a long tubular stem, a casing of heat conducting material sealed on the end of said stem, a liquid tight closure for the outer end of said casing, an

arbor rotatably mounted in the stem and having its end projecting into the casing. a shaft carried by the closure at the end of the casing, said shaft projecting into the casing towards the end of said arbor and in axial alignment therewith, and a duplex bimetallic coil wound from a strip of bisaid casing being filled with a heat conducting liquid, anda liquid sealing ring surrounding said .aroor and yieloingiy held against a seat atthe with respect to said 'seat.

5. A bimetallic thermometer comprising a long slender stem, a casing of heat conducting material mounted on said stem, an arbor rotatably mounted in the stem and having its end projecting into the casing, a bimetallic coil in said casing and attached to said arbor, said casing being filled with a heat conducting liquid, and a liquid sealing ring surrounding said arbor and yieldingly held against a seat at the end of said casing adjacent to said stem, said seat and ring having coacting faces lying in a plane normal to the axis of the arbor whereby said ring is capable of limited lateral movement with respectto said seat, a hollow indicator head attached to the outer end of said stem, said head being airtight, the outer end of' the arbor projecting into said head, and indicating means in said head operatively connected with said arbor.

6. A thermo-responsive bimetallic coil comprising two layers of metal of uniform thickness having embossed therefrom a reinforcing rib extending lengthwise of the metal from which the coil is formed, said rib decreasing in rigidity from the outside of the coil inwardly.

7. A thermo-responsive bimetallic coil comprising two layers of metal of uniform thickness in which the outer turn or turns are deformed transversely of their length so as to make them stiifer than the inner-turns.

8. A duplex bimetallic coil for a temperatureresponsive device comprising two spiral coils arranged in axial alignment and firmly connected together at their outer ends, one of said coils being anchored at its inner end to a. fixed support, and the other coil being anchored at its inner end to a part to be moved, the relationship of the-metals in the two coils being reversed so that in one coil the metal of the greater coaavaooa emcient of expansion is on the outside, and in the other coil the metal of the greater coemclent of expansion is on the inside, each of said coils having a reinforcing rib extending lengthwise of the metal from which the coil is formed, said ribs being of varying depth and deepest near the outer ends of the coils.

9. A duplex bimetallic coil for a temperatureresponsive device comprising two spiral coils arranged in axiil alignment and firmly connected together at their outer ends. one of said coils being anchored at its inner end to a fixed support, and the other coil being anchored at its inner end to a part to be moved, the relationship of the metals in the two coils being reversed so that in one coil the metal of the greater coei'flcient of expansion is on the outside, and in the other coil the metal of the greater coefficient of expansion is on the inside, each of said coils being variably stiffened from'the outside inwardly, the stiffening decreasing in rigidity from the outside inwardly.

10. A thermo-responsive bimetallic element comprising two layers of metal of different coeflicients of expansion and each of uniform thickness, and firmly united together, said element having embossed therefrom a reinforcing rib extending lengthwise of the element, said 12 embossed rib varying in depth longitudinally 80 as to give the element differential rigidity longitudinally thereof.

HERMAN SCHLAICH.

REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENTS Num-er Name Date 430,853 Hodgson June 24, 1890 1,058,290 Corey Apr. 8, 1913 1,292,991 Barstow Feb. 4, 1919 15 1,479,784 Bosworth Jan. 8, 1924 1,725,607 Wolfard Aug. 20, 1929 2,000,092 Norwood May 7, 1935 2,019,221 Hastings Oct. 29, 1935 2,058,426 Drake Oct. 27, 1936 2,109,169 Field Feb. 22, 1938 2,131,544 Welland Sept. 27, 1938 2,144,915 Derby Jan. 24, 1939 2,180,362 Leonard Nov. 21, 1939 2,230,711 Yon Feb. 4, 1941 2,241,902 Drapeau May 13, 1941 2,284,082 Bloch May 26, 1942 2,317,831 Vaughan Apr. 27, 1943 2,365,487 Murray Dec. 19, 1944 

